Consumer Voice over Internet Protocol (VoIP) services are steadily gaining popularity. In some cases a consumer has a subscription with one network service provider for data Internet and VoIP services. A residential gateway and a customer premises equipment (CPE) device such as, for example, a VoIP phone receives service from the same network service provider. In other cases a consumer has a subscription with a first network service provider for Internet service and additionally a subscription with a second network service provider for VoIP service. In this situation the residential gateway accesses the Internet via the first network service provider while the CPE receives service via the second network service provider. In such circumstances, the CPE accesses the second network service provider through the residential gateway served by the first network service provider.
Many network service providers use dynamic Internet Protocol (IP) addresses. These network service providers change the dynamic IP addresses of subscribers from time to time (e.g., periodically) through their Dynamic Host Configuration Protocol (DHCP) servers. Typically, the first network service provider updates or changes the IP address of a subscriber by sending a new IP address to the subscriber's residential gateway. The second network service provider (which did not change the IP address) typically receives a notification of the IP address when the CPE registers the new IP address with the IP Multimedia subsystem (IMS) of the second network service provider.